Process of concentrating milk and product



R. WHITAKER ET AL PROCESS OF CQNCENTRATING MILK AND PRODUCT Filed June 26, 1951 TIME.

I I800 SEC I800 sec l76v5 a sec.

1500 see 142" I500 see 6265" a sec I I I70 I50 M m w TEMP -3o 21,600 sec TIME SEO. 25,000

lopoo I50 900 SEC.

I I L I I30 12F INVENTORS TEMP BY Ema/411 I VHJTAKER 3 1- E Aux/imam 63 fife/ea AITOR/WFMS Patented Dec. 22, 1953 UNITED STATES ATENT OFFICE PROCESS OF CONCENTRATING'MILK AND PRODUCT Randall Whitaker, Sayville, and Alexander 0. Herro, Oakdale, N. Y., assignors to National Dairy Research Laboratories, Inc., Islip, N. Y., a corporation of Delaware Application June 26, 1951, Serial No. 233,566

sales of sterilized evaporated milk. However, it

is generally conceded that although evaporated milk is reconstitutable with water to produce a a fluid milk, milk, the reconstituted product, difiers pronouncedly in flavor from fresh milk, described as having a, cooked. or boiled flavor.

This flavor undoubtedly is due to the processing conditions. In the production of sterilized evaporated milk, it is essential to preheat the milk to at least 180 F. in order to prevent the formationof grain during sterilization. Thereare; sterilized evaporated milk is usual1y.pre pared first by preheating the fresh milk to 180 F. or higher, holding at this temperature for-from to minutes, concentrating at temperatures ranging from to 180 Fl, but usually in"the range from to F., standardizingby the addition of water, filling into cans, preheating from 200 to 210 F. and finally sterilizing at from Many processes have been proposed forcon oentrating fluid milk to produce a concentrated milk for distribution to consumers and home consumption, but these processes have not been successful commercially, primarily because at some stage ofthe process a cooked flavor appears. Even though the milkmay'be successfully concentrated without developing a" cooked flavor, when the concentrated milk is pasteurized, a cooked flavoralmost invariably results.

To avoid this difficulty, it has been proposed that the milk be pasteurized before concentrating. However, most localities require pasteur'iza: tion just before bottling so thatftl'lis .xlifidien't has a limited application. "Moreover; when a pasteurized milk is concentrated, icookedil'fiavor,

'22 Claims. (01. 99-55)" 2 pasteurizing fluid milk without development of an off flavor has not been forthcoming.

Accordingly, it is an object of the present invention to provide a process applicable on a commercial scale for concentrating fluid milk and pasteurizing the concentrate to form a product'which, when reconstituted to its original volume by addition of water, possesses a flavor fully comparable to, and in most instances, substantially the same as, the pasteurized original fresh milk.

.It is a further object to provide a pasteurized concentrated .milk which possesses no oil flavor, such as a cooked flavor, which can be stored for long periods of time, and which, despite a lower butter fat and calorie content, than regular cream, frequently can be used as a substitute for cream.

, It is a further object of the invention to provide a. pasteurizedconcentrated fluid milk which can be reconstituted with Water to produce a fluid milk having a better flavor than pasteurized homogenized whole milk from the same raw milk supply.

Itis also an object of the invention to provide a concentrated milk which, on reconstitution with water, will produce a fluid milk in which the butter fat and the solids-not-fat contents will be in optimum relationship to each other from the standpoint of flavor. v

The process contemplated by the invention includes preheating and concentrating the milk and, in one featured embodiment, pasteurizing the concentrated milk. vIn another embodiment, the milk may be homogenized after concentration and following orpreceding pasteurization.

In this process, the above objects are accomplished by controlling within specified limit the tions require higher temperatures than others.

Furthermore, use of a high temperature in one stage may necessitate the use of a lower tempera ture in another stage in order to hold at a minimum the time during which milk is held at ele vated temperatures. The maximum temperature at which the milk can be maintained in the process of the invention is about 176.5 F., and this temperature is permissible in the pasteurizing stage only; the milk is not held at this temperature for more than seconds. Preferably, the milk is never heated to a temperature above about 165 F. at any stage of the process, and it is always desirable to use the lowest temperatures and shortest times commensurate with the result desired and the available equipment.

The inve'ntion'thus has as its basis an appreciation of the closely controlled conditions under which water must be removed in concentrating milk, as well as in the procedural steps related to concentration, including preheating. the milk prior to concentration and pasteurizing the concentrated milk, if the milk is to be concentrated thus retain the flavor andnutritioh values'of fresh whole milk. Especially noteworthy is an 4 in such cases. It will be understood that only raw milk is concentrated in accordance with the invention, pasteurization being carried out on the concentrate; it is, however, preferred to employ a raw milk having a 10W bacterial count.

In accordance with the invention, concentrated milk may be made from any combination or mixture of milks as starting materials, but usually it is made either from 1) whole fluid milk or (2) cream, or (3) by separating whole fluid milk into cream and milk, concentrating the skim milk or thecreain or bothand then recombining them.

Several variations may be introduced in proc- -essing each of these three basic starting materials. For example, in the case of (l) and (2) the ratio of the butter fat to milk solids-not-fat ofcr'eam, orby addition or removal of milk solidsnot fat in the form of fluid or concentrated skim appreciation of the intimate relationship between the temperature and the time during which that temperature is applied. The limits of time and temperature must be rigorously observed and indeed'ar'e very critic'alif the development of an off flavor, Suchaycooked or boiled flavor, is tops avoided. 7 7

The time duringwhich the milk is held at any temperature is inversely related to the tempera ture; The relationship between time and temperature for each of three stages of the process of the invention is shown in the drawings, in which:

Fig. 1 is a graph of the'relationship between time and temperature in the preheating of the milk prior to concentrating; maxima and minima curves/A and B, respectively, enclosing a shaded area I which represents the operative process conditions which must be observedin this stage;

Fig. 2 is a graph of the relationship between time and temperature in the concentration of the milk, curve C marking'the maximum limits of time and temperature which must be observed in thisstep, any conditions inthe area below curve C representing the operative'process conditions; and s v V Fig. 3' is a graph of the're'lationshipbetween time and temperature in the pasteurization of the concentrated milk, maxima and minima curves D and 'E respectivelyenclosing" a shaded area III which represents operative process conditions which must be observed in this step.

The process may be carried out employing usual dairy equipment, including afstainlesssteel vacuum'pan and drop tank forthe concentration operation. The milk should not be permitted to contact copper or copper alloys at any stage of the'process. All equipment used should pref erably be of stainless steel, and stainless steel was used in the examples set forth later herein.

The invention is particulai'ly applicable tomilk; In -thecaseof (3), variations include the separate preheating treatment of a high fat and a 1owfat milk followed by combining the two,

' separate concentration of a high fat and a low fat milk followed by combining the two, or concentration of either the high fat or the low fat milks, followed by combining the two. I

Before considering details of the essential process operations of the invention, it should be stated that there are two general methods of applying the process of the invention: the batch method and the continuous method;

In the batch method, th'e milk is drawn into the vesselin which it is to be preheated; concentrated or pasteurized, and the operation begun. If the operation involves concentrating the milk, as the volume of milk decreases; it is the custom to introduce more unconcentrated milk into the vessel. The operation is continued until the contents of the vessel have reached the desired temperature, concentration or have been pasteurized, as the case maybe; at which time the application of heat is discontinued, and the treated product withdrawn.

In a batch system, it is apparent that in the preheating and pasteurizing operations the temperature-and time of treatment are ascertainable within the precise limits, and can be carefully controlled. In the concentrating operation, how ever, all of the milk in the vessel has not been subjectedto the treatment for the same length of time, that which was drawn into the vessel last being under treatment for the shortest period of time. It has been found that asatisfactory concentrate, free from cooked flavors, is obtainable when the temperatures indicated by curve C of Fig. 2 are not exceeded but the treatment times indicated by the curve are computed as the average time during. which the milk in the vessel is held at the indicated temperature.

In a continuous-operation, milk is drawn into the vessel in which it is to be preheated, concentrated or pasteurized and the operation begun. Untreated milk is continuously admitted-into the vessel during operation and when themilk in the vessel has reached the desired temperature or concentration, or is pasteurized, removal of milk is begun. Thereafter, the rate of flow of untreatedmilk, admitted to the vessel is kept equal, or at least approximately equal, on a solids basis to the rate of withdrawal of milk from the vessel.

In this case, all of the milk in the vessel has not been subjected to the treatment for the same length of time, and some of the milk may remain in the vessel for quite long periods. It has been found that a satisfactory concentrate free from cooked flavor is obtained when the maximum temperatures indicated by the curves A, C and D of Figs. 1, 2 and 3 respectively are never exceeded, but. thetimes indicated by the curves are. computed as the average time that the milk is subjected to the treatment in question.

The process operations of the invention will now be considered in greater detail. It will be understood that the treatment times referred to in the following discussion are to be regarded as average times, when applied to batch concentration or continuous preheating, concentration or pasteurization of milk. At the start of any of the operations to be considered the milk is brought to. an operating temperature as quickly as possible and in any event within about twenty minutesv if the operating temperature is about 140 F. or below, and within about ten seconds if the operating temperature is 160 to 176 F. with proportionate times at intermediate temperatures. At the conclusion of the operation the milk is cooled to a storage temperature, or is brought to the next operating temperature, if a change in temperature is required, as quickly as possible, and in any event within about twenty minutes if the operating temperature" is about 140 F. or below and within about ten seconds if the operating temperature is 160 to 176 F. with proportionate times at intermediate temperatures. This is in accord with the general theory of the invention that the total treatment time of the milk beyond that specified in the preheating, concentrating and pasteurizing operation of the invention, should be kept at a minimum, and is taken into account in the operating conditions established in the process of the invention.

The preheating treatment Prior to concentration, the milk is preheated at a temperature and for a time sufficient to reduce the activity of the lipase and also preferably to reduce the bacterial count sufiiciently to prevent spoilage and/or development of rancidity at a later process stage. This preheating is essential because later steps are conducted at temperatures and under conditions which may favor bacterial growth and lipase-induced rancidity. The temperature and'time required'to accomplish this will, of course, depend upon the bacterial count and lipase concentration of the milk, and this will vary considerably even from batch to batch taken from the same milk supply. However, in all cases the time and temperature are chosen within the shaded area I of Fig. 1.

The minimum heat treatment is indicated in Fig. 1 by curve B which runs along a logarithmic line from 6 seconds at 162.5 F. to 120 seconds .(2 minutes) at 120 F. The minimum treatment will sufficiently retard the activity of lipase to prevent the development of rancidity during later stages of the process, but may have little effect on the bacterial count. The maximum heat treatment will also materially reduce the bacterial count, and is represented by curve A which runs along a logarithmic line from 6 seconds at 162.5 F. to 1500 seconds minutes) at 142 F.

v The maximum preheating temperatures and heating times indicated by curve A in Fig. 1 must be closely observed to prevent development of "cooked flavors,

The concentrating of the preheated mizki i The maximum times and temperatures permitted during the concentrating operation if de-' velopment of cooked flavors are to be avoided are shown by curve C of Fig. 2. Any conditions represented in the area below curve Care operat'ive. The curve extends logarithmically from 900 seconds at 150 F. to 21,600 seconds (6 hours) at 120 F. No minimum temperatures are specified, but even when temperatures below 120 F. are employed, the time should never exceed 6 hours.

Because milk cannot readily be concentrated under atmospheric pressure at the maximum temperatures imposed in order to prevent the development of a cooked flavor, it is usually found convenient to concentrate the preheated milk under reduced pressure. The pressure used, as those skilled in the art are aware, controls the boiling point; lowering the pressure lowers the boiling point of milk, and hence lowers the'concentrating temperature. A pressure not higher than 2 to 4 p. s. i. absolute is usuallysatisfactory, but very low pressures can be used for concentrating at lower temperatures, for example, for concentrating in the frozen state.

While low temperatures, 1. e. 40 to F., may be employed, unless the bacterial count is negligible following preheating it is usually desirable to concentrate at a temperature which discourages bacterial growth, i. e. about to F. This consideration is important in a commercial process, in view of the length of time required to concentrate large volumes of milk.

Concentration of the milk is continued to the desired solids content. However, as the solids content increases, protein coagulation may oc-- our and care should be exercised to reducethe concentrating temperature to prevent excessive thickening of the product in the concentrating vessel. Milk concentrated to'a 50% solids content is subject to protein coagulation at about F., and milk of 60% solids content is subject to this condition at about 115 F. Although heating at temperatures which may induce protein coagulation may improve the keeping qual' ity of the concentrate, and lead to an increase in viscosity, facilitating ship-ping, heat coagulation should not be permitted to occur untilconcentration is complete. I

Selection of the solids content of the concentrate will be governed by several considerations.

There are advantages'in continuing the concentration of the milk to a solids content of from- 40 to 62.5%, at least initially. The rate of bacterial growth is considerablybelow normal" (for milk) in a concentrated milk of high solids content, i. e., from 40 to 62.5%, and therefore this product may be held for long periods of time under refrigeration, below 40 F., without pasteurization. In fact, during storage the bacterial count in many instances has been observed to go down rather than increase,"as the following data show:

concentrated cream and concentrated skim milk.

From the standpoint of flavor acceptability there is an optimum solids-not-fat content for any given butter fat content. This relationship 10 with water, preferably before pasteurization, and contains 9.9% butter fat and 24.25% solids-non fat. When reconstituted with twice its volume of water, it yields a milk containing 3.5% butter is shown in the following table: fat and 8.58% solids-not-fat. The same concen- TABLE II QPTIMZUM RATIOS OF BUTTER FAT AND I V trated reconstituted .Vith 1.6 to 1.7 Volumes S I N of water yields a composition lying in the optin mum range for flavor, as shown in Table II.

- a A concentrated milk which can be reconstituted A t r Tmlm fififi r e s l i tia ed oi eofi with water to produce a product having a better cenmted 111k flavor than the pasteurized and homogenized original whole milk can be prepared by separating gg Solids-not-fat g Solids-not'fat milk into skim milk and cream of at least 20% fat content, condensing the skim milk separately Percent Percent at temperatures and pressures within the ranges g-g set forth heretofore, homogenizing the cream at j 5 3, a temperature in the range from 120 to 165 F. 8 2: 3? under a pressure of 3000 to 5000 p. s. i., sufficient L to cause a clumping of the butter fat globules in The table shows that for milk containing 2.5% the a as vldenced appreclable butter fat the most acceptable flavor is crease in viscosity, recombining the unhomogetained when the solids-not-fat content is in the mzed concentrated Skim milk with the homoge' ran b t e 10,2 and 101% whereas if th nized cream and pasteurizing without further butter fat content is 4.5%, the most acceptable homogenization. Rooonstituted m k p p ed flavor is obtained when the solids-not-fat confrom this concentrated product has a better tent is 9.2 to 9.7%. flavor than one prepared by concentrating and The ratio of butter fat and solids-not-fat of homogenizing whole milk under precisely the y conceiiiirated m of t invention c be same conditions as the cream in the previous probroilght W h the ranges c ith 111 Table II 7) cedure and then pasteurizing. The reason for by addltlon 9 cream or Sk1 m mflk to the difference in flavor is not yet fully underceim'ated or who m be amusifed stood. Preparation of a product of this type is prior to concentration. Cream is added to millustrated in Example 10 crease the relative butter fat content, and skim milk to increase the relative solids-not-fat con- The ggif exir-nples a g of g tent of the reconstituted product to meet the J process? 8 mven 1on.an of evanous pro ratio requirements ucts which may be obtained thereby.

Taste comparisons have shown that milks reconstituted from a concentrated milk with water EXAMPLE 1 fi? Wlth Pi and fanmg Whole raw milk is heated at 143 F. for 5 min- Wl m 8 range 0 composltmns covered by utes in order to decrease the activity of the lipase. Table II are all equally acceptable. In all taste reheated milk is then transferred to a comparisons made until now between a concenp h b d concentmt d at 127 F trated milk diluted to an optimum composition vacuum 0 am er D t within the proportions of the above table and i i 2 urmg comm freshly homogenized pasteurized milk, the milks non the mflk 1S clrculated through a heat were either equally acceptable in flavor or the changer Whose heat exchange surfaws are kept reconstituted milk was preferred. In no case has at After about 4 hours the content the fresh milk been preferred over the reconstihas reached about 40%, and the milk 1s removed tuted concentrated product. Table III shows refrom the vacuum chamber, d lllted w1th water to sults of taste tests which are typical: 34.15% total solids and homogenized at 120 F.

\ TABLE III I i I Calculated Degree of "a "I i ce P obability iiiiii has. iiiiiiiiiar Preferred an 751a oltastersl like fig Sam ity,in- 24 2 9 B12 choice am 1 it f samples p p 6 standard Se S p e p I errors 1 standard ence 1' errors 0 Percent 4 Percent 27 1 3.1 0.194 30 5o -3 n 2.2 2.77, 26 0 2.2 2.78 27 41 2 B 1.7 8.91 11 1 6.4 2 10 27 51 '2 B 3.0 0.27 32 1 1.9 5.74 34 44 4 B 1.1 27.13 32 0 2.0 4.55 so 45 1 B 1.0 31.73

' cv vcase was regular pasteurized milk.

an on. or, as indicated in Table II.

A preferred concentrated product in accordance with the invention is prepared from whole raw milk by preheating at 145 F. for 15 minutes, concentrating at 125 F. to a solids content somewhat above 34.15%, homogenizing at F. and i a pressure of 2500 p. s. i., and pasteurizing at 7 for 30 minutes. The concentrated product is brought to a solids content of 34.15%

' ass was pasteurized homogenized milk in Which the ratio of butteriat to solids-not-fat had been adjusted tr and ate. pressure of 3500 p. s. i. It is then pasby dilution 75 which they were prepared:

R4AB1ZE IY \Goncentrate'd (loncentrated Opncentrated m1l-k,.1;econmilk, reccn- .Rasteutizefl milk stituted with stituted with whole milk 2 vol.'.w ater ii vol. Water r 1: Per P nu P 111; Per r 1'. quart quart er-ce uart er-ce quart (gnu) we ght (gm) we ght. Kgm') weight (gum weight 9.9 i 34.2 3.6 51.3 5.18 34.2 "3. 5 .940 .30. 8. :3. l6 d6. 6 4. 7i 30. 8 3. 16 13.3 Z 46.0: 4. 72 68.8 6.95 46.0. .4..72 1:95. 16;? 0.7 10.1 1.02 6.7 0.7 34.15 117.7 12.08 no.2 17.86 117.7 12.08 165.85: 858.3. 87. '92 813. 2 82.14 858.3 87.92 'Totalweighuflf 1,036.0" 976: 1 000.0 976.0

'Theconcentrate (34:1'5% solids) has a slightly salty/taste and is characterized by remarkable keeping qualities. 'It freezes atabout 27"F. If it is stored'in an ice boxor mechanical refrigerator at a temperature above its freezing point but below 40 R, it will usually maintain its fresh flavor for about four weeks-but samples prepared in the manner outlinedtabmze have been known to iremain ,"SWEBlL and dresh' tasting for .from six toeight weeks.

Elate counts made by standard bacterial math- .05 on concentrated milk produced under com mercial conditions in accordance with the specifioationsflescribed herein usually .show less than 1000 colonies ,per,.g1.am. Out of 12 consecutive lots commercially produced, -.Q l .Y one showed 120!) per gram. the IestbeingIOOO Or'less. Pasteurized flu d .milk usuany contains'frpm :1000 to 10000 colonies per gram.

The concentrate can be fortified with any nutritionally desirable amountpf vitamin D. For example, 400 U. S. P. units of vitamin D can be addedperreconstituted uaut.

When reconstituted with twov .vohimes of .cold water, .this product has. the same characteristics as to body, homogeneity and flavor as regular pasteurized homogenizedm'ilk. The curd tension of the reconstituted concentrated milk is of "the same order as that of regular pasteurized homogenized milk.

Table V below give the results of taste tests which show reconstituted concentrated milkmade according to the process described in this exam pie to be indistinguishable from fresh pasteurized whole milk. These tests were conducted in the following manner: A sample of pasteurized, homogenized whole .milk and a sample ;of reconstituted concentrated milk wer presented to each v taster. The samples were identified only by number. A third sample was presented to each taster, who was told that it was identical with one of the first two samples. Each taster was .asked to indicate which of the first two samples the third matched. The results were evaluated statistically.

TABLE V Calculated I Probabil- Number deviation Number gr ggi 22x32 who-were from fig g of g h g unable to equality occurrence 'tgs-ters s l fii on selecti n gg g gg staglamp .of i V A errors y 'z Percent :38 D SL 5,0..00 70 "32 U 0.7 48.39 .68 .33 34 1 O. 1 "50. 00 42 33 0 3,1. .73 33 44 39 0 GL5 50.00

The results of theitable :aboue show-that the possibility of the selections having been made by chance is great, indicating that the panel of tasters was unable to distinguish .b etween thetwo milks.

.-A number of taste-tests were also for the purpose of finding a preference, ii :any, between pasteurized, homogenized whole uni-1k and-milk reconstituted from concentrated :milk prepared according to this invention. Table shows the results of :some'of typical tests. In this tes taster-s were iven one sample :of :nasteuuizerl. homogenized -whole .milk'zand :one sample 17M reconstituted concentrated milk. Each'wasasked which'sample he preferred.

The results show equal --:accepta bility for the two milks.

Raw whole milk .is separated into skim milk and cream containing approximately 40 1.050% butter fat. The skim milk is conducted through .a heat exchanger where it is heated to just below -162.5 F. and held at that temperature for '6 seconds in order to reduce the lipase activity and bacterial count, after which it is immediately flashed into a vacuumc'hamber. The skim is circulated from the vacuum chamber through a heat exchanger supplied with hot water at 165 and then back into the vacuum chamber which is helda-t a temperature of F. and a pressure of 1.25 p. s. i. absolute, until '7'? to 81% of the water contained therein is removed. The product consequently will have :8 solids content of .from.3.0% to.34%.

The cream :is heated to 150 F. and held at that temperature vfor approximately '2 minutes in order to reduce its lipolytic activity, after which it is mixed with the concentrated skim milk.

Water or whole milk is added so that the final product will have about 10%.ibutter fat and 34% total solids content after which the mixture is heated to approximately F. and homogenized at a pressure of approximately 2000 p. s. 1.,

EXAMPLE 3 The butter fat and solids-not-fat content of whole milk is adjusted by addition or removal of cream or skim milk so that the ratio of butter fat to solids-not-fat in the milk is 10:277. The resulting product is heated at 145 F. for 10 minutes and then drawn into a vacuum pan equipped with heating elements within the vacuum chamber. The milk is then. concentrated at 110 F. under a pressure of 1.25 p. s. i. absolute within 6 hours to a solids contentof 6 .5%, after which it is removed from the vacuum chamber and cooled to room temperature.

Raw Whole milk is incorporated in the concentrated milk to bring its solids content to 37%, after which it is heated to 140 F., homogenized at 3000' p. s. i., pasteurized at 155 F. for'30 minutes and cooled to 40 F.

The concentrated product has outstanding keeping qualities. It can be reconstituted with 2 volumes of water to produce a fluid milk substantially indistinguishable in flavor from an unconcentrated pasteurized homogenized fluid milk. It can also be reconstituted with 1 volume of water to produce a viscous extra-rich milk product having a butter fat content of about to 5.5%, for use in coffee, on fruits, cereals and desserts.

EXAMPLE 4 Whole raw milk is heated to a temperature above 160 but not exceeding 162.5 F. for 5 seconds in order to reduce lipolytic activity and then drawn into the first effect of a double effect evaporator operating at an absolute pressure of not over 3.3 p. s. i., where it is heated to 145 F. and a proportion of the water content thereof removed, and then into the second efiect of the evaporator operated at an absolute pressure not over 1.7 p. s. i. and a temperature of 120 F. The milk in the evaporator is maintained in motion at sumcient velocity to ensure a rapid transfer of heat from the heating surfaces within the evaporator to the milk. -After the milk concentration has reached 40% solids, within about 1 /2 hours, the milk is withdrawn from the evaporator, brought to a solids content of 34.15% by addition of water, homogenized at a temperature of 120 F. and 2500 p. s. i., pasteurized at 175 F.

'for 16 seconds and cooled to 2'7 F.

The product can be reconstituted with 2 volumes of water to produce a fluid milk possessing substantially the same flavor as pasteurized homogenized whole milk and useful for drinking.

cooking and any of the other uses. of ordinary fluid milk. w I EXAMPLE 5 Whole raw milk of normal quality is separated intoskim milk and cream. The cream and skim milk are heated separately at from 14-0 to 145 for 2 minutes. The skim milk thereaiteris condensed as set forth in Example 2, mixed with suflicient cream to bring the solids content to 38% and the butter fat to homogenized at 140 F. and 1500 p. s. i., pasteurized at 155 F. for minutes and cooled. I

' The product can be reconstituted with 1 part growth. At any time 01' water to produce a product having a butter fat content of about 5.2%. It may also be reconstituted with 2 volumes of water to produce a milk slightly richer in flavor and body than the Whole milk from which it was prepared.

The concentrated product may be stored at 30 F. for 4 weeks. or more Without developing an off flavor.

EXAMPLE 6 Whole raw milk is heated at 155 F. for one minute .in order to reduce lipolytic activity and then condensed as set forth in Example 3 to a total solids content of 60%. The concentrated milk is then heated at 121 F. for 15 minutes after which there is a noticeable increase in its viscosity. The concentrated milk is then cooled to 40 F. it may be held at this temperature for several days without spoilage due to bacterial before bacterial growth has increased to an undesirable degree, the concentrated milk can be mixed with water, cream, fresh whole milk, fresh skim milk, or mixtures of the above to reduce its solids content to 40% or less, heated to a homogenizing temperature, homogenized, pasteurized and cooled to 40 F. as set forth in any of the preceding examples.

EXAMPLE '7 Whole raw milk is separated into skim milk and cream. The skim milk is heated at a temperature of 155 to 160 F. for 12 seconds and then drawn into the first eifect of a double effect evaporator operating at an absolute pressure of not over 3.3 p. s. i. where a portion of the water content thereof is removed by heating at about 145 F. for 10 minutes. The milk is then drawn into the second efi'ect of the evaporator operating at an absolute pressure of not over 2 p. s. i. and a temperature of about 125 F.- where it is condensed to a total solids content of from 45 to 50%. The total time of concentration should not exceed 4 hours. The concentrated milk is then removed from the second eiTect of the evaporator and heated at F. for a few minutes until there is a noticeable increase'in its viscosity, and then cooled. The resulting concentrated skim milk may be held in cold storage at 27 F. just above its freezing point for three weeks or more without undesirable bacterial decomposition.

Whenever desired. for use, the concentrated skim milk may be mixed with cream, which has previously been heated to F., and water or fresh milk, to adjust the ratio of butter fat and Solids-riot-fat to 1:285, and the mixture heated} homogenized, pasteurized and cooled. The prod uct reconstitutes with water to give a milk containing 3.5% butter fat and 10% milk solids-notfat.

Instead of heating the creamto a temperature at which lipase activity is reduced, before mixing with the concentrated skim milk, the cream, water, and/ormilk may be heated to at least 140" F. for a time sufiicient to reduce lipolytic activity in the cream (and in the whole'milk if whole milk is used) before the mixture is homogenized.

EXAMPLE 8 Whole milk is separated into skim milk and cream. The cream is heated to atleast but not over F. and homogenized at a pressure or aces-sis 1-5 "The skim is preheatedandconcentrated by the method "set forth iii-Example 2.

' The homogenized cream is coniliined "the l tingu ishable in flavor from whole raw-milk which has been heated to 138" and homogenized.

concentrated skimarrd the are teurized at 155 for dll'minutes a d cooled to 5 WhOle is p fid $11170 Skim milk a d M? E. "or lower without iurtl rer homogenization. cream having b The Cream is I ucongen 'blta'ted milk, many, qgcmg timfigm heated and concentrated as set. forth in'Example with water to its original solids content, will taste 1 to a butter fat Content of 4 and then is a richer than pasteurized-hcmegenized milk made d to at least 155 F. but not over 165 F. and from the same raw milk supply. It may also be homogenized BI a pressure 0 50753900 95 reconstituted with asmall 'vol-urne of water to Sufficient 17851156 u p 0 Tthe 31111151181 produce an extra-rich *miik with a --'ereamier globules inthe Cream a elfidenced y an pp flavor than ordinary pasteurized homogenised Oiable in Viscosity milk, I The skim milk is concentrated separately -:as

M-ilk reconstituted from concentrated milk Set/forth n Example made by pas'teurizing a mixture of homogenised The homogenized concentrated cream amiiconcream and concentrated skim milk according to e ated sk m l ar mixed, teu d a the process described in Esample '3isdistinguish 155 F. for 30 minutes, andcooled to 40 F.'w'rth able from pasteurized homogenized whole milk out further fl fiz t fl and "from concentrated prepared by ocn- This concentrated milk upon reconstruction cent/rating whole milk without clumping the int h W fi O s al'sfl mnteni? w ll 15 globules in the cream. Table e snow-s the ericher than pasteurized homo niz d milk m sults'of 'diiference-preierenoe tests conducted n from the Same raw m lk p o uct bmyw the following manner: :Dasters 'W6l 8glvl31'l-& be reconstituted with a (small volume of water sample of milk reconstituted from concentrated 5 to produce an extra-rich milk product -of-excelmllk made according to Example 8, and :a sample lent flavor. of the-'milk with which it was being compared. By the process of this invention, concentrated Each taster was asked to indicate his preference milks may be produced with various shutter fat between the. two, after which he tasted a third and total solids content so that, lonrreconstzltutim sample which was identical with one of the first withfrom twoto five volumes ofwa'ter, the resulttwo and asked whichof the first two samples it i-ng product will meet the butter Iat rand soltids matched. not-fat requirements tor'f fluid milk in any area.

'T-ilnLr. v11

cu a 2 3222325 Probabilitv Number -lvlatch'edi Unable gggfiggg Preferred Preferred NO Brc I Eleviationof chance ol'i'asters like unlike match fly sciec'fion Sample 511111919 efioice ferred frornequdh occurrence ,samplesj p s mp gangland Iless'than; A B sample 1ty,n1 of prefermums g standard ence i I GP-POTS Percent 3 l .Percent 1 100ml 71 o 4 2 =0.-eo5- as as 5 A 1.7 an 2; 77 45 32 "c 1 5 13:36 4a: 31 1 s A 1. 4 16115 3.30..-- :45V o i 1 22.13 29 c, A L8: v.19 4..77 44 .33. 0- 1 3 19.36 a a2 4' A 1.4 16.15

7 Sample A inev-erycasc was reconstitutedfrom lconcentratedimilk made by mixing homogenized cream with concentrated skgmmilk'as setforthm Example 8. Sample 13, with -which Sample A was compared, was as .Iollows in cach compauison 1. Fresh homo. .past. whole milk. '2. 'Reconstituted concfwhole milk. 73. Reconstitlited :conc. whole milk.

4. :Roconstituted cone. :milk madeiromconcskimmilk rchomogen rred'with'homogenized cream.

331e, results of .these tests show that m'ilkreconstituted from concentrated milkmade with cream in which the .fat globules have been clumped .is distinguishable from and preferred slightly over the milks with which it was compared.

EXAMPLE 9 Whole raw milk is concentrated to a total solids content between 34% and 35% in an evaporator which previously has been thoroughly cleaned and preferably treated with a. sanitizing agent to reduc the probability of bacterial infection. The concentration is accomplished-at :a

temperature of 134 to 138 F. and at absolute til This concentrate can be reconstituted with two volumes of .water to produce a fluid milk :indis- When reconstituted with less than "the amount of water prescribed a partly concentrated milk is obtained particularly suitable'for use on cereals and fruit.

The concentrated milk may be used "full strength for creaming coffee and tea.

Carbonated water in any flavor may be mixed with the concentrated milk to produce a variety of beverages.

More milk solids may be "incorporatedinto cream soups and sauces, casseroles and puddings when concentrated milk used. The concentrated milk may also be used to prepare homemade frozen desserts.

To a dairy processer the concentrated milk .furnishes a substantial saving in timerequired to homogenize, pasteurize, :fill and stack milk containers, as well as a substantial reduction in containers, refrigerated storage space and delivery bulk. Because of the increased keeping properties of the concentrated product, there also existsis had. In addition, there are the variety of novel uses in new recipes, etc. which natural fluid milk does not possess. The product is especially welcome to those individuals whose diets require large quantities of the proteins of the high biological value of those found in mllk.

lhe concentrated product having a. solids content of from 20 to 50% by weight is particularly useful in the production cated.

We claim: 1. In the process of preparing a concentrated mill: which includes the steps of preheating the milk at a temperature at which lipase activity is produce mill; substantially indistinguishable in flavor from the original unconcentrated milk after pasteurization.

2. A process of preparing a concentrated lacteal fluid which comprises preheating the lacteal fluid at a temperature within the range from about 162.5 to about 120 F. for from about 6 seconds to about 1500 seconds as defined by the shaded flavor-imparting lacteal fluid constituents with attendant development of cooked flavor are avoided and a concentrated lacteal fluid is produced which can be reconstituted with water to produce a lacteal fluid substantially indistin guishable in flavor from the original unconcen- 'trated lacteal fluid after pasteurization.

3. A lacteal fluid concentrate-produced by the process of claim 2 which isreconstitutable with in order to reduce the bacterial count in addition to reducing lipase activity.

A process in accordance with claim 2 which includes homogenizing the concentrate at a temperature above about F. and a pressure within the range from 1500 to 5000 p. s. i.

6. A process .in accordance with claim 2 which cream is concentrated.

7. A process in accordance with claim 2 in which raw whole milk is concentrated.

8. A: process in accordance with claim 2 in which skim milk is concentrated.

9. A process in accordance with claim 2 which includes concentrating the lacteal fluid at least to one-third its volume.

10. A process in accordance with claim 2 which includes concentrating the lacteal fluid to a solids content of at least 60%.

11. A process of preparing a concentrated milk which comprises preheating the milk at a temto about 150 to about 1800 seconds, whereby damage of flavorimparting milk velopment of at a temperature within 120 to about F. at a pressure within the range from 3000 to 5000 p. s. i. combining the homogenized cream with to about 150 about 1800 seconds as defined by the shaded area of Fig. 3. 

1. IN THE PROCESS OF PREPARING A CONCENTRATED MILK WHICH INCLUDES THE STEPS OF PREHEATING THE MILK AT A TEMPERATURE AT WHICH LIPASE ACTIVITY IS REDUCED, CONCENTRATING THE MILK UNDER REDUCED PRESSURE AND PASTEURIZING THE MILK, THE IMPROVEMENT WHICH COMPRISES MAINTAINING THR TEMPERATURE AND DURATION OF THE TREATMENT IN THE PREHEATING STEP WITHIN THE SHADED AREA OF FIG. 1, IN THE CONCENTRATING STEP AS DEFINED BY CURVE C AND WITHIN THE AREA BELOW CURVE C OF FIG. 2 AND IN THE PASTEURIZING STEP WITHIN THE SHADED AREA OF FIG. 3, WHEREBY DAMAGE OF FLAVOR-IMPARTING MILK CONSTITUENTS WITH ATTENDANT DEVELOPMENT OF "COOKED" FLAVOR ARE AVOIDED AND A CONCENTRATED MILK IS PRODUCED WHICH CAN BE RECONSTITUTED WITH WATER TO PRODUCE A MILK SUBSTANTIALLY INDISTINGUISHABLE IN FLAVOR FROM THE ORIGINAL UNCONCENTRATED MILK AFTER PASTEURIZATION. 